1. Field of the Invention
The present invention relates to an image forming material employable for display, for a color proof in color proofing and as a non-silver salt photosensitive film for printing.
2. Description of Prior Art
There are known image forming materials used in various fields of print, photograph and fine processing of metal, which comprise a photosensitive resin layer containing a photopolymer and a coloring material provided on a support (or temporary support in a transfer type image forming material).
The image forming materials having the above structure can be used for color proofing. A color proofing sheet can be obtained by exposing an image forming material (i.e., photosensitive sheet) to light through a color separation halftone film for each color plate, developing it to form a color separation image on a photosensitive resin layer, and transferring the color separation image to an arbitrary support (i.e., image receiving surface).
As an improved image forming material comprising two-layer structure, there have been proposed image forming materials wherein a coloring material-containing organic high-molecular polymer layer (sometimes called a coloring material layer) is interposed between the support and the photosensitive resin layer without incorporating any coloring material into the photosensitive resin layer. Examples of such image forming materials include those described in Japanese Patent Provisional Publications No. 47(1972)-16124, No. 52(1977)-89916, No. 55(1980)-117142, No. 55(1980)-12752 and U.S. Pat. No. 4,472,494. The image forming material comprising such three-layer structure that a coloring material-containing layer (or organic high-molecular polymer layer) and a photosensitive resin layer are independently provided as described above gives advantages as compared with the conventional image forming materials. In more detail, the improved image forming material is kept from lowering in sensitivity which is raised by lowering of exposure efficiency of the photosensitive layer caused by the co-existing color material in a conventional image forming process which comprises exposing an image forming material to light and developing the exposed material to form a color image. Further, when the image forming material is utilized as a non-silver salt lith type film (film having a high resolving power) for printing, the contrast of the obtained image is made very high. In other words, it gives appropriate halftone dot reducibility.
After the image forming material is exposed to light, the photosensitive resin layer is usually treated with a developing solution and the organic high-molecular polymer layer (coloring material layer) is developed (i.e., etched) to form an image. The image forming material can be classified into a positive type wherein the exposed portion of the photosensitive resin layer is removed by development and a negative type wherein unexposed portion is removed by development.
There have been previously proposed image forming materials in which the photosensitive resin layer and the corresponding underlaying layer, that is, the organic polymer layer (coloring material layer) are allowed to be simultaneously developed and removed. Such image forming materials are described in Japanese Patent Provisional Publications No. 52(1977)-89916 and No. 55(1980)-12752 and U.S. Pat. No. 4,472,494. Such image forming materials have an advantage in that the development (develpment of exposed portion or unexposed portion and etching of the coloring material-containing polymer layer) can be simultaneously conducted by a single treating solution (e.g., alkaline solution, etc.) so that the development step is simplified.
While the image forming materials of the three-layer structure type have the advantage described above, there is a disadvantage in that the underlaying layer, that is, the organic polymer layer (coloring material layer) is apt to suffer from side etching in the developement step for forming a color image at a degree higher than the photosensitive resin layer on the underlaying layer.
FIGS. 1-(1) and 1-(2) show sectional views wherein the above-mentioned side etching occurs in the case that a color image is formed by developing the image forming material after exposure to light. FIG. 1-(1) shows the sectional view of the side-etching observed in a positive type image and FIG. 1-(2) shows the sectional view of the side-etching observed in a negative type image. In FIGS. 1-(1) and 1-(2), numeral 1 indicates a support, 2 indicates an organic high-molecular polymer layer (coloring material layer), and 3 indicates a photosensitive resin layer. As shown in FIGS. 1-(1) and 1-(2), the color image portion 4 undergoes side etching 5 in the course of development so that the size d of the color image is reduced from the size D of the halftone dot of the original image. Accordingly, when a multi-color type color proof is prepared using such a color image, it is impossible to obtain precise reproduction of the colors of the original image.